TiO2 photo catalyst was prepared in presence of nano SiO2 and Hydroxy Propyl Cellulose (HPC) by sol gel method with Titanium Tetra IsoproPoxide (TTIP) as titanium precursor. Additional effect of HPC in preparation of nano catalyst, and photo catalyst properties measured and characterized by FT-IR, FT-Raman and SEM. The catalyst size and structural properties of the film were determined by .-Ray Diffraction (.RD). The nano particles of TiO2/SiO2 with HPC contained anatase phase in advance. The surface area measured by the Brunauer, Emmett and Teller (BET) method. Presences of Ti and Si in the nano structure were confirmed by Scanning Electron Microscopy (SEM) equipped with Energy Dispersive .-ray (ED.) spectroscopy. Photo catalyst properties of TiO2/SiO2 examined at first for decomposition of Methyl Red as azo dye, and then for degradation of 5ppm diazinon solution as an organo phosphorous insecticide pollutant in marine source, (Caspian Sea water). Concentration of diazinon during of degradation by TiO2/SiO2 photo catalyst was monitored by UV-Vis spectrophotometery. The insecticide degradation occurred within 105 min of photocatalytic treatment.